It is common practice in the formation of concrete walls to erect a form system which includes parallel spaced panels interconnected by a tie system which traverses the space between the panels. Usually, the central members of the tie system remain embedded in the concrete. The primary advantage of such an arrangement is that the forces resulting from the deposition of the initially plastic concrete are balanced out between the opposite form panels, and thus require a minimum of bracing from the outside. Such bracing can be limited to maintaining the vertical orientation of the assembled form system.
The forces resulting from the placement of the plastic concrete are extremely high, as this material generates a liquid pressure of approximately one hundred sixty pounds per square foot per foot of depth, the latter corresponding to the height of the wall. The increased pressure at the lower extremeties of the form system result in a closer spacing of cross-tie components in this area, which are commonly a foot or so apart at the bottom of a wall of substantial height, increasing to perhaps three feet apart at the top. A contractor that is particularly active in this type of construction will normally be using metal form panels sufficiently short in lateral dimension to be handled conveniently by lifting equipment, and installed in edge-to-edge relationship to form a substantially continuous panel system having a coplanar forming surface. When parallel panel groups are installed in this manner, and the tie systems properly installed, concrete can be deposited between the panels according to standard procedures. One of the most effective cross-tie systems that have been developed for securing such panels has involved the use of threaded rods of high-tensile steel positioned in the central area between the paralled form panels, these being connected at opposite ends to bolts that traverse the panel system, and are secured to it to transfer the stresses involved. When the concrete has hardened sufficiently, the bolts are rotatably disconnected, and the form panels "stripped", leaving the central rods embedded in the concrete. Recesses formed by the inward projection of the bolts, which expose the ends of the threaded rods, can either be left exposed, or filled as may be desired.
This type of tie system has been rather difficult to incorporate in metal form panels, as a result of problems involved in properly engineering the points where the bolts traverse the relatively thin sheet metal of the forms. Stress transfer must accommodate the relatively heavy concentration at the ties, which receive the collected stresses distributed over the area of the panel. In addition to these structural problems, the erection and stripping procedures involving the installation and removal of large numbers of the bolts presents a problem in time and convenience. A significant feature in common in most standard form panels is the presence of a relatively heavy edge flange at the meeting edges of the panel units, which is commonly used to receive cross-fastenings securing the panels laterally together to prevent leakage of the concrete between them. The present invention utilizes this common feature in a structure which requires no further modification of standard form panels, and eliminates entirely the matter of providing special stress-concentration reinforcement at the point where the bolts for the tie system traverse the panel units.